Telephone system



9 Sheets-Sheet l INVENTOR THOMAS F. GROCKER BY 26mm/M ATTORNEYS Dec. 9,1941. T. F. cRocKER TELEPHONE SYSTEM Filed April 11, 1940 9 Sheets-Sheet2 mmmb @N NWN NQ u NVENTOR THOMAS F. OROCKER M Mun@ ATTORNEYS BY ,OMM/IMFiled April 1l, 1940 9 Sheets-Sheet I5 THOMAS FA CROCKER ATTORNEYS Dec.9, 1941. 1'. F. cRocKER TELEPHONE SYSTEM Filed April 11, 1940 9SheeCS--Sheeil 4 .NSE n @@v/ Em YnQI ATTORNEYS T. F. CROCKER TELEPHONESYSTEM Dec, 9, 1941.

9 Sheets-Sheet 5 Filed April 1l, 1940 THOMAS F. CROGKER TTORNEYS.

Dec. 9, 1941. T, F. cRocKER TELEPHONE SYSTEM 9 sheetssheet s Filed April11, 1940 @mu E@ am? vmmm. m6@ n Im uw @www mg @S k .w Q

lD/5 TRIBU ToR Kwon u mvw/ m mv@ f m MIN@ w @5U oo@ QE n Et@ wmdz x EuQ@ lNvENToR THOMAS F. CROGKER 'M M ATTORNEYS www *mmm Dec. 9, 1941. 'r.F. cRocKER TELEPHONE SYSTEM Filed April 11, 1940 9 Sheets-Sheet 7 THOMASF. CROOKER ATTORNEYS 9, 1941- T. F. cRocKER TELEPHONE SYSTEM 9Sheets-Sheet 8 Filed April l1, 1940 ATTORNEYS 9 1941- T. F. cRocKERTELEPHONE SYSTEM Filed April 11, 1940 9 Sheets-Sheet 9 l |9||)|.\Nm u RMmm. 4 hmmbx m Tl T .R am@ m m. N F E S vv A Qmmm m wma@ .vmm l mmm @IMSi @a NE# e Num/J www www. .TTI mmilfmwm f Nwmh @mmm :wma Sm@ ml mm2 f ml "mm fr @Q3 i Sm l QSI s@ o C o o o o o o o o v o o o amy c Sm Qmo mo mww o Sm@ man Sm 4 @om IV IMI. "Ce SC mwtm mmz otmn @mu/ laD Qm @mu mmm@PatentediDea 9, 1941 UNITED TELEPHONE SYSTEM yThomas F. Crocker,Chicago, Ill.,4 assignor to Associated Electric Laboratories, Inc.,Chicago, Ill., a corporation of Delaware Application April 11, 1940,Serial No. 329,071I

56 Claims.

The present invention relates to telephone systems and more particularlyto improvements in private automatic branch exchanges.

A private automatic branch exchange or P. `A. B. X is usually associated-with a central oice by way of a nunber of two-Way trunk lines extendingtherebetween and conventionally comprises an operator position, a numberof telephone stations having lines extending thereto and switchingapparatus. Ordinary local calls between the various telephone stationsin the P. A. B.` X are completed by the switching apparatus underthevcontrol of the subscribers at the telephone jstations without theassistance of the operator at theoperatr position; while both incomingand outgoing trunk calls are completed betweenthe central oice and thevarious telephone stations in the P. A. B. X either directly by or withthe assistance of the operator at the operator position.

It is an object of the present invention to provide in a telephonesystem of the character noted an improved arrangement for selectivelycontherebetween; wherein the P. A. B. X comprises necting ay number oftrunks to an operator position and for selectively controlling theoperation of a number o`f trunk switches individually associated withthe trunks to seize a number of lines accessible thereto. e v

Another object of the invention is to provide in 4a telephone system ofthe character noted an improved switching arrangement selectivelyoperativefto establish local and trunk connections and to hold trunkconnections.

Another object of the invention 'is to provide in a telephone system animproved arrangement for selectively marking a number of lines and forcausing switching apparatus toseize marked ones of the lines.

Another object of the invention is to provide in a telephone system animproved arrangement for selectively marking any one of a number oflines for selection by switching apparatus having access thereto, whichmarking arrangement is'selectively controlled by both manual means andautomatic means.

A further object of the invention is to provide in a telephone system animproved arrangement for releasing a rst switch train operated toestablish a connection to a given line when a second switch train isoperated to establish a connection to the given line.

A further object of 'the invention is to'provide in a telephone systeman improved arrangement for identifying a calling line included in anestablished connection extending to an operator position. l

A further object of the invention is to provide in a telephone system animproved switching arrangement for establishing connections betweencalling lines and an operator position, which switching apparatus isselectively controlled in accordance with the classes of calls on thelines.

rA further object of the invention is to provide in a telephone systemimproved switching ap.. 4

an operator position, a number of telephone stations having telephonelines extending thereto and switching apparatus. The switching apparatusprovided in the P. A. B. X comprises a number of trunk switchesindividually associated with the trunk lines, a number oi local linksand a position switch associated with the operator position. f l

ln, accordance with one feature of the invention, the P. A. BrXcomprises an operator position, a plurality of groups of lines eachincluding a plurality ofsubgroups of lines, an automatic switchassociated with the operators p0- sition and having access to the lines,and a key set associated with the operator position and including anumber of keys. Also, the arrangement comprises means controlled byinitial operation of one of the keys in the key set for ,marking acorresponding onel of the groups of lines, means controlled by furtheroperation of one of the keys in the key set for marking a correspondingone of the subgroups of lines in the marked group of lines, meanscontrolled by a nal operation of one of the keys in the key set formarking a corresponding one of the lines in the marked subgroup of linesinthe marked i -means including the switch for establishing a connectionbetween' the operator position and the selected line.

In accordance with another feature of the invention, the P. A. B. Xcomprises la number of trunk switches individually terminating thetrunks extending vbetween. the central oiiice and the P. A. B. X, thelines extending to the telephone stations in the P. A. B. X beingaccessible 'the operator position for causing `the one oi the trunkswitches terminating the one trunk to seize any one of the lines,thereby to complete a connection between the one trunk and the one lineincluding the operator position, and means controllable from theoperator position for disassociating the one trunk from the operatorposition, thereby to complete a connection between the one trunk and theone line excluding the operator position.

In accordance with another feature of the invention, each of the trunksextending between the central oiiice and the P. A. B. X comprisesnormally connected central oice and branch exchange sections; and atrunk circuit and a line circuit are individually associated with eachtrunk, the trunk circuit being operative in a rst manner to disconnectthe central omce and branch exchange sections of the trunk and toconnect a bridge to the central oflice. section of the trunk and toconnect the branch exchange section of the trunk to the line circuitandopera-.

tive in a second manner to reconnect the central yomce andbranchexchange sections of the trunk and to disconnect the bridge fromthe central oice section of the trunk and to disconnect the f branchexchange section of the trunk from. the line circuit. Also, thearrangement comprises means for completing a connection between thecentral office and any one of the telephone stations including thetrunk, means at the one telephone station for selectively controllingover the trunk the manner of operation vofthe trunk circuit, and meanscontrolled when a bridge is connected to the central oice section of thetrunk for retaining the connection to the central oiiice. Also, the P.A. B. X comprises a number of switching links, means controlled when thebranch exchange section of the trunk is connected to the line circuitfor causing the -one of the switching links to seize the line circuitand for retaining the one switching link operated, and meanscontrollablerfrom the one telephone station over thel trunk and the linecircuit for causing theswitching link to seize another of the telephonestations, thereby to complete a connection between the one telephonestation and the other telephone station. Also, the trunk circuit isoperative in a further manner to cause a signal to be transmitted to theoperator position, thereby to indicate the presence of a recall on theestablished connection between the central oice and the one telephonestation; and means is provided at the one telephone station foroperating the trunk circuit in the further manner over the trunk.

In accordance with another feature of the invention, the P. A. B. Xcomprises a marking network which is so connected and arranged that itis manually controllable from the key set associated with the operatorposition and automatiin order respectively to cause any one ofthelines'to be marked for selection or to cause the line seized by theoperated switching link to be marked for selection.

In accordance with a further feature of the invention, the switchinglinks are so connected and arranged that when a line is marked forselection by the marking vnetwork due to the seizure of the line by anoperated one of the switching links, the one switching link isautomatically released when the trunk switch terminating one of thetrunks operates to seize the marked line.

In accordance with a further feature of the invention, the arrangementcomprises a link distributor adapted to connect. the switching links tocalling ones of the lines in a predetermined order, each of theswitching links including control apparatus governable over a callingone of the lines connected to the switching link and a register, thecontrol apparatus included in each of the switching links beingselectively governable to cause the link to be connected to any one ofthe called lines and selectively to operate the register included in theswitching link, the register included in each of the switching linksbeing selectively operative to mark the link as occupied by diierentclasses of calls. Also, a position switch is associated with theoperator position and has access to the switching links. Control ymeansis provided at the operator position which is operative in a iirstmanner to cause the position switch to seize one of the switching linksmarked as occupied by acall of a first class and operative in a secondmanner to cause the position switch to seize one of the switching linksmarked as occupied by a call of a second class.

In accordance with a further feature of the invention, an identitydevice is associated with the operator position which is so connectedand arranged that it is controlled jointly by the operation of one oftheswitching links to seize a calling line and the operation of theposition switch to seize the one link in order to identify the callingline in the event the calling line has a call thereon of a iirst class.Furthermore, when the trunk switch associated with one of the trunks isoperated to seize the calling line previously seized by the switchinglink mentioned, the identity device is released.

Further features of the invention pertain to the particular arrangementof the circuit ele- Varrangement of a telephone system, including acentral ofIice and a private automatic branch exchange, embodying thepresent invention; Figs.

.-2 to 9, inclusive, taken together, illustrate the details of a' systemhaving incorporated therein the features of the invention, as brieflyoutlined above; and Fig. 10 illustrates the mode of comf bining Figs. 2to 9, inclusive, of the drawings to form a unied system.

Description of the apparatus incorporated in `the telephone system.

Referring nowniore particularly to Fig. 1 of the drawings the telephonesystem there illusltrated comprises a central ofiice 50, a privateautomatic branchexchange or P. A. B. X 60 and aplurality of two-Waytrunk lines, including the trunk line 490, extending therebetween. Thecentral ofiice 50 and the' P. A. B. X 60 are of the automatic dial type,the P. A. B. X 60 comprising an operator position 800 and a number oftelephone stations including the stations TI and T2. Further the P. A.B. X 60 comprises a number of local links, including the local linkillustrated, and a distributor 680 for assigning idle ones of the locallinks to the use of the telephone stations. For example, the local linkillustrated includes a local finder switch 600 and a local connectorswitch 100. Also a trunk circuit and a trunk finder switch areindividually associated with each of the trunk lines, the trunk circuit400. and the trunk finder switch 500 being individually associated withthe trunk line 490.

A telephone line having al line circuit individually associatedtherewith extends to.each telephone station in the P. A. B. X; thetelephone lines 605 and 150 respectively extending to the telephonestations TI and T2 and the line circuit 690 being individuallyassociated with the telephone line 605. Further an auxiliary linecircuit is individually associated with each trunk circuit, theauxiliary line circuit 494 being individually associated with the trunkcircuit 400. Finally an operator key set and marking circuit 200, anidentity lamp and trunk finder start circuit 300, and an operator finderswitch 900 are associated -with the operator position 800.

Each of the local finder` switches, such, for Zexample, as the localfinder switch 600, each of the local connector switches, such, forexample,I as the local connector switch 100, and each of the trunkfinder switches, such, for example, as the trunk finder switch 500, hasaccess to each telephone line in the P. A. B. X. Also the operatorposition 800 has direct access to 'each trunk line extending between thecentral office and the P. A. B. X and to each trunk finder switch.Further the operator position 800 has access by way of the operatorfinder switch 900 to each local link.

Preferably `each of the local links in the P. A. B. X ls' identical tothe local link illustrated which comprises a local finder switch 600 anda local connector switch 100, as previously noted. The'nder switchf600,as best shown in Fig. 6, YVcomprises a switching mechanism 6I0 of the200- point Strowger type including a carriage provided with a firstwiper set,v including the wipers 6I3, 6I4 and 6I5, a second wiper set,including the wipers 6I6, 6I1 and 6I8, and three control wipers 6I I,6l2 and 6I9. It is noted that the Wipers 6I3, 6I4 and 6I5 of the firstwiper setand the wipers 6I6, 6I1 and 6I 8 of the second wiper set arecapable of both vertical and rotary movements; the control wipers 6I I,and 6I9 are. capable of vertical movements; and the control wiper SI2 iscapable of rotaryI movement.. Further the mecha- LA,nism 6I0 comprises acircumierentially disposed main contact bank provided with two sectionsrespectively associated with the first and second wiper sets, twovertical control contact banks anism 6I0 the rstand second wiper setsrespectively have access to first and second groups of,

one hundredlines each respectively terminated by the flrst and secondsections of the main contact bank. Also the mechanism 6I0 is providedwith a vertical magnet M62I for moving the first and second wiper setsthereof in the vetrical vdirection, a rotary magnet M623- for moving thefirst and second wiper sets thereof in the rotary direction, and arelease magnet M625 for releasing the first and second wiper setsthereof and for causing these wiper setsto be returned to their normalpositions. Finally the mechanism 6I0 has two sets of switch springs S625and S621 operatively associated therewith which are controlled inaccordance with the movements of the first and second wiper sets thereofin a manner more fully described subsequently.

Also the finder switch 600 comprises a number of relays including twoswitching relays R640 and lR650, a hold relay R660 and an identity relay4 R610 connected and arranged in a manner more fullyldescribeldsubsequently. y

The connector switch 100, as best shown in Fig.

r 7, comprises a switching mechanism 110 of the ZOO-point Strowger typeincluding a carriage provided with a first wiper set, including thewipers 11|, 112 and 113. and a second wiper set, includ-- ing the wipers114, 115 and 116. It is noted that the wipers 11|, 112 and 113 of thefirst wiper set and the wipers 114, 115 and 116 of the second wiper setare capable of both vertical and rotary movements. Further the mechanism110 comprises a circumferentially disposed main contact bank providedwith two sections respectively associated with the first and secondwiper sets. Accordingly, in the mechanism 110, the rst and second wipersets respectively have access to first and second groups of one hundredlines each respectively terminated by the first and second sec- Vtionsof the main contact bank. Also the mechanism 110 is provided with avertical magnet M111 for moving the first and second wiper sets thereofin the vertical direction, a rotary magnet M118 for moving the first andsecond wiper sets thereof in the rotary direction, \and a release magnetM119 for releasing the rst and second wiper sets thereof and for causingthese wiper setsA to be returned to their normal positions. Finally, themechanism 110 has a number of sets of switch springs S180, S182 and S185operatively associated therewith which are controlled in accordance withthe-movements of the first and associated with the control wipers 6Hand.6l9,.

second wiper sets thereof, in a manner more fully Adescribedsubsequently.

Also the connector switch includes a con trol switch 190 of the Minortype including three rotary wipers 19|, 193and 195 provided withindividually associated rotary contact banks '192, 1.94 and 196. Alsothe controlswitch 190 is provided with a rotary magnet M191 for movingthe wipers noted in the rotary direction and a release magnet M198 forreleasing the wipers noted and for causing these wipers to be returnedto their normal positions. Finally the control switch 190 includes twosets of switch springs S191 and S198 which are controlled in accordancewith the movements of the wipers noted in a manner more fully describedsubsequently.

Also the connector switch 100 comprises a number of relays including aline relay R100, a battery supply relay R105, three transfer relaysR1I0, R120 and R130, a busy relay R140, a cutoi relay R and twoswitching relays R160vand wiper I1.

the first and second wiper sets respectively have,

poses it is noted that the connection and ar-l rangement of avdistributor of the type of the distributor 680 is shown, in thecopending applil cation of Edward S. Peterson, Serial No. 233,021,A

filed October 3, 1938.` Also a marking network 596, shown in Fig. 6, ,isassociated with the distibutor 080 in order to initiate operationthereofhen a call is initiated on one of the telephone I lines `extending to atelephone station in the P. A.B. X.

Preferably each f the trunk finder switches is identical tothe trunkfinder switch 500 individually associated with the trunk line 590, shownin Fig. 5, which comprises a switching mechanism 5I0 of the 200 -pointStrowger type includtimerrelay R640, afi answer relay R460 and a controlrelay R420, connected and arranged in a manner more fully describedsubsequently. Further the trunk circuit 400 comprises a line lamp L406,a busy lamp M05 and ka. hold lamp L4M.

Preferably, each of the line circuits is identical to the line circuit690 individually associated with the telephone line 605 extending to thetelephone station TI, shown in Fig. 6, which comprises a line and cutoffrelay R690 connected and arranged in a manner more fully describedsubsequently. Preferably, each of the auxiliary line circuits isidentical to the auxiliary line circuit 595 individually associated withthe trunk circuit 400, shown in Fig. 4, which auxiliary line circuit isconnected and arranged in any suitable manner, such, for example, as theline circuit 690 individually associated with the telephone line 005extending to the telephone stal tion TI.

lng a carriage provided with a first wiper set,

including the wipers 5II, 5I2 and 5I3, a' second wiper set, includingthe wipers Elfi, 5I5 and 5I6, and two control wipers 511 and 5I8. It isnoted that the wipers 5I I, 5I 2 and 5I3 of the first wiper set and thewipers 5m, 5I5 and 5I 5 of the second wiper set are capable of bothvertical and rotary movements; the control wiper 5I8 is` capable ofvertical movement; and. the control wiper 5H is capable of rotarymovement. Further the mechanism 5I0 comprises a circumferentiallydisposed main contact bank provided with two sections respectivelyassociated with the first and second Wiper sets, a vertical controlcontact bank associated with the control wiper 5I8 and a rotary vcontrolcontact bank associated with the control Accordingly, in the mechanism'5I0 access toI rst and second groups of one hundred lines each,respectively terminatedl by the iirst and second sections of the maincontact bank.

Also the mechanism 5I0 is provided with a vertical magnet M5I9 formoving the` lrst and second wiper sets thereof in the verticaldirection, a

rotary magnet M52! for moving the rst 'and second wiper sets thereof inthe rotary direction, and a release magnet M523 for releasing the rstand second wiper sets thereof and for causing these wiper sets to bereturned to their normal positions.' Finally, the mechanism 5m has twosets of switch springs S520 and S525 operatively associated therewith,which are controlled in accordancel with the movements of the first andsecond wiper sets thereof in a manner more fully described subsequently.

Also the finder switch 500 comprises a, number of relays including ahold relay R505, a connect relay R500, a cutoff relay R550, atrunk-offer relay R560, a start relay R510, a busy relay R500,

two switching relays R5I0 and R520, a step relay R585 and a transferrelay R590 connected and arranged in a manner more fully describedsubsequently.

Preferably each of the trunk circuits is identical to the trunk circuit400 individually assol t ring-up relay R445, a transfer relay R050, a

Each of the telephone stations in the P. A. B. X 60 is provided withstation equipment including a telephoneinstrument, a ringer, a pushbutton and calling device or dial.

The operator position 800comprises, as shown in Figs. 4 and 8, a trunkcircuit provided with a set of position keys including an informationkey X850, an information hold key X855, a common ytrunk key X850, acommon trunk 1hold key X865, a trunk offer key X840 and a release keyX810. Also the trunk circuit at the operator position 800 is providedwith an individual trunk key and an individual trunk hold key individualtoreach trunk line extending betweenthe central'oice 50 andthe P. A. B.X 60, the individual trunk key X080 and the individual trunk hold keyX590 being individual to the trunk line 490 extending between thecentral ofhce 50 and the P. A. B. X 50. operator position 800 comprisesa telephone instrument including a transmitter I and 'a receiver 802, acalling device or dial 805, a repeater `9, is of the'rotary type andcomprises six rotary wipers 001, 903, 905, 901, 909 and SII providedrwith individually associated rotary contact banks 902, 900, 906, 008,9I0 and 9I2 and a rotary magnet M9I5 for driving the wipers noted.Further the operator finder switch 800 comprises a number of relaysincluding a stop relay R940,y

a control relay R950, a trunk relay R960, an information relay R9'I0 andtwo pilot relays R980 and R500, connected and arranged'in a manner morefully described subsequently.

` The operator key set and marking circuit 200, shown in Fig. 2 andassociated with the operator position 800, comprises ten respectivedigit keys XI to X0, inclusive, an error key XII and a\ number of relaysincluding three transfer relays R220, R225 and R230, an error relayR210, three control relays R240, R250 and R260, a start relay R215, arelease relay R265, a rst group of marking relays IC and 2C, a secondgroup of marking relays ID, 2D, 3D and 0D, anda third group of markingrelays-IU, 2U, .3U and 4U.

It is noted that the digit keys KI to X0, inclui sive, are operatedsuccessively to set up a hundred'digit, a ten digit and a unit digit,thereby Also the trunk circuit at the cluding the marking relays IC and2C to register the hundred digit, to cause the second group of nlmarkingrelays including the marking relays ID,

2D; 3D and 4D to register the ten digit, and to cause the third groupof-marking relays including the marking relays IU, 2U, 3U and 4U toregister the unit digit. Furtherthe operator key set and marking circuit200 is connected and arranged with respect to the trunk circuit at thefirst operator position 800 in a manner more fully describedsubsequently.

The identity lamp and trunk iinder start unit 300, shown in Fig. 3 andassociated with the operator position 600, comprises a first group ofidentity lamps including the identity lamps CLI and CL2, a second groupof identity lamps including the identity lamps DLI to DLIO, inclusive,and a third group of identity lamps including the identity lamps ULI toULIO, inclu sive. It is noted that the rst group of identity lampsincluding the identity lamps CLI and CL2,

" the second group of identity lamps including the identity lamps DLI toDLIO, inclusive, and the third group of identity lamps including theidentity lamps ULI to ULIO, inclusivefrespectively correspond` to thehundred, ten and unit digits of the directory number of a callingtelephone .station in the?. A. B. X. Finally the indentity lamp andtrunk iinder start unit 300 comprises a number of relays including astart relay R3I0 -and two marking' relays R320 and R330 connected andarranged in a manner more fully described subsequently.

A better understanding of the connection and arrangement of theapparatus incorporated in the telephone system will b'e facilitated froma consideration of the detailed operation of the various pieces ofapparatus incident to the completion of diiierent calls and the handlingof v applying ground potential by way of the resistor various calls atthe operator position 800, as will appear hereinafter.

'Local call from one station to another station in the P. A. B. X

A local call which is to be extended from one from its switchhook. Forexample, in extending a call. from the telephone station TI to thetelephone stationT2 the call is first initiated at the station TI byremoving the receiver of the telephone instrument thereat from itsswitchhook, thereby to 4complete a bridge path including the receiver ofthe telephone instrument between the line conductors C606 and C601 ofthe telephone line 605 extending to the telephone station TI. When thisbridge path is'completed between the line conductors of the telephoneline 605 a circuit is completed for energizing in series the windings ofthe line and cutoff relay R690 included in the line circuit 690individually associated with the telephone line 605. This circuitextends from ground by way of the lower winding of R690, the contacts692, C601, the bridge path between the line conductors C601 and C606,C606, the contacts 69|, and the upper and'intermediate windings of R690to battery. When energized over the above-traced circuit the line andcutoi relay R690 operates partially, thereby to complete, at thecontacts 695, an obvious path for applying ground potential to the startconductor C691 and to complete, at the contacts 693,

649 of the marking `network 696 to the start conductor C688 extending tothe Ldistributor 680, and

an obvious path `for applying" direct ground potential by way of theconductor C698 to the iirst contacts in the vertical control contactbaul-rsv of the local finder switches. The application of groundpotential to the start conductor C686 initiates operation of thedistributor 680 and the application of direct-ground potential to theilrst` contacts in the vertical control contact banks of thelocali-Inder switches marks the telephone line 605' as terminating inthe rst level of the main contact banks of the local nder switches.

The distributor 680 is of the preselective type and operates to selectanother idle local link as soon as the finder switch of a previouslyselected local link operates to find a calling telephone line after ithas been taken for use. Assuming that the distributor 680 has previouslyselected the local link illustrated to be taken for use at this time,the distributor 680 operates to cause ground potential to be applied tothe start conductor C682, thereby to complete an obvious circuit forenergizing the winding of the hold relay R660.l The hold relay R660 thenoperates to interrupt, at the contacts 66I, a point iny a multiple pathfor applying groundpotential to the all-linkbusy conductor C661, and tocomplete, at the contacts 662, \an obvious path for applying groundpotential to the control conductor C618 of the trunk 615. The previouslymentioned path for applying ground potential to the all-linkbusyconductor C68I in the local iinder switch 600 extends, when completed,yfrom ground by way of the contacts 66I and 626 to the all-linkbusyconductor C68Ij.l IAlso the hold relay R660 completes, at the contacts663, obvious multiple circuits for energizing\the lower windings of theswitching relays R640 and R650, thereby to render each of the switchingrelays extremely fast to operate in the event the upper winding there--of is energized. Further the hold relay R660 prepares, kat the contacts661, a circuit traced hereinafter forA energizing the vertical magnetM62I and prepares, at the contacts 666, a circuit traced hereinafter forenergizing the rotarymagnet M623. The distributor 680 then operates t'ocause ground potential to be applied to the vertical conductor C686,thereby to complete the previously mentioned circuit for energizing thevertical magnet M62I, this circuit` extending from the grounded verticalconductor C686 by way of the contacts 661 and M62I to battery. Whenenergized over the above-traced circuit the vertical magnet M62Ioperates to drive the rst and second wiper sets of the mechanism 6 I 0one step in the vertical direction and to complete, at the contacts 622,an obvious path for applying ground potential to the interrupterconductor C685. The application of ground potential to the interrupterconductor C685 causes the distributor 680 'to interrupt the applicationof ground potential to the vertical conductor C686, whereupon thevertical magnet M62I restores to interrupt, at the contacts 622, thepreviously mentioned path for applying ground potential to theinterrupter conductor C685. Accordingly, the vertical magnet M62Ioperates intermittently, thereby to drive the iirst and second wipersetsof the mechanism 6I0 step by step in the vertical direction untilthe control wiper 6I9 ductors C608 and C609 of the telephone 1ine605.

engages a contact in the associated vertical control contact bank havingdirect ground potential thereon, whereupon an obvious path is completedfor applying ground potential to the test conductor C681 extending tothe distributor 680. In the present instance, the first and second wipersets of the mechanism 6I0 are driven only vertical control wiper 6|9engages the first contact in the associated vertical control contactbank having ground potential thereon. The application of groundpotential to the test conductor C681 causes the distributor 680 tooperate; thereby to interrupt the application of ground potential to thevertical conductor 'C686 and to apply ground potential to the rotaryconductor C686.

The application of ground potential to the rotary conductor C684completes the previously mentioned circuit for energizing the rotarymagnet M623, this circuit extending from the grounded rotary conductorC684 by way of the contacts 666, 650'and 661 and M623 to battery.

When energized over the above-traced circuit' the rotary magnet M623operates to drive the first and second wiper sets of the mechanism 610one step in the rotary direction and to cornplete, at the contacts 624,an obvious path for applying ground potential to the interrupterconductor C685. This application of ground potenupper winding of theswitching relay R650, thereby positively to prevent operation of thelatter relay at this time. relay R640 interrupts, at the contacts 648, apoint in a circuit traced hereinafter for energizing the releasev magnetM625 and completes,

one step in the vertical direction, whereupon the` at the contacts 646,a connection between the rotary conductor C684 and the/guard conductorC683, this connection extending from the rotary conductor C684 by way ofthe contacts 666, 650, 646 and 664 to the guard conductor C683. When therotary conductor C684 isA connected to the guard conductor C683,operation of the distributor 680 to control the local finder switch 600is arrested, whereupon the distributor 680 operates automatically-,toselect for use another idle one of the local links.

Finally, upon operating, the switching relay R660 completes, at thecontacts 66|, 643 and 644, connect-ions between the conductors of thetrunk 630 extending to the rst wiper set of the mech- Aanism 6I0 and thetrunk 615 extending between the local finder switch 600 and the localconnector switch 'l00.V When the trunks' 630 and 615 are connected a lowresistance circuit is completed for energizing the intermediate windingtial to the interrupter conductor C685 causes the distributor 680 toremove the application of ground potential to the rotary conductor C686,whereupon the rotary magnet M623 restores to interrupt, at the contacts626, the previously mentioned path for applying ground potential to theinterrupter conductor C685. Accordingly, the rotary magnet M623 operatesintermittently, thereby to drive the first and second wiper sets of themechanism 60 step by step in the rotary direction until either thecontrol wiper 6 l 5 or the control wiper 6|8 of the respective rst andsecond wiper sets engages the control conductor of a calling telephoneline having battery potential thereon. In the present example thetelephone line 605 is included in the first section of the main contactbank of the mechanism 6I0. Accordingly, when the control wiper 6|5 ofthe first wiper set of themechanism 6I0 engages the con.

tact of the contact set in the first section of the main contact bank ofthe mechanism 640 terminating the control conductor C608 of thetelephone line 605, a circuit is completed for energizing the upperwinding of the switching relay R640. This circuit extends from ground byway of the contacts 694 and 695, the start conductor C691, C698, thevertical control wiper 6l9, C639, the upper winding of R660, the controlwiper 6|5, C608,'the contacts 693 and the intermediate winding of R690to battery. When energized over the above-traced circuit the switchingrelay R640 operates exceedingly fast, thereby to complete, at thecontacts 665, a holding circuit for energizing the intermediate windingthereof, this circuit extending from ground by way of the contacts 662,the control conductor C618 of the trunk 615, the contacts 651 and 645and the in'- tacts 649, a point in a circuit for energizing the of theline and cutoi relay R690, this circuit extending from the groundedcontrol conductor C618 of the trunk/615 by way of the contacts 651 and644, C633, the wiper 6I5, the control conductor C608 of the telephoneline 605, the contacts 693 and the intermediate winding of R690 tobattery. When the intermediate winding of the line and cutoff relay R690is thus energized this relay operates completely, thereby to interrupt,at the contacts 696, the previously traced path for applying groundpotential to the start conductor C691 extending to the marking network696 in order to arrest operation of the disj tributor 680. Further theline and cutoff relay R690 interrupts, at the contacts 69! and 692, thepreviously traced circuit for energizing the windings thereof across theline conductors C606 and C601 of the telephone line 605, thereby toclear the telephone line 605 of impedance elements. At this time groundpotential appearing upon the control conductor C608 of the telephoneline 605 is applied to the control conductor C609 thereof, thereby tomark the telephone line 605 as busy to the local connector switches andthe trunk finder switches having access thereto.

Also it is noted that when the carriage of the mechanism 6|0 is drivenone step in the vertical direction the set of switch springs S625 andS621 are actuated. More particularly, the contacts 626 and 621 of theset of switch springs S625 are respectively actuated into disengagementand into engagement; while the contacts '629 and 628 ofthe set of switchsprings S621 are respectively actuated into disengagement and intoengagement.

Further it is noted that the distributor 680 operates in order to selectanother idle local link for use only in the event ground potentialappears upon the all-link-busy con-ductor C68| and in at least one ofthe local nder switches, ground potential being removed from theall-link-busy conductor C68l in the local nder switch 600 at this timedue to the operated condition of the set of switch springs S625, aspreviously noted. Also ground potential is applied to the guardconductor C683 in the local nder switch 600, thereby to prevent thedistributor 680 from4 Also the switching ,C618 ofv the trunk 615 duetothe busy condition of the local finder switch 600. The path for applyingground potential in the nder switch 600 to the guard conductor C683extends from ground by way of the contacts 628 of the set of switch-springs S621.and the contacts 665 to the guard conduotor C663, the holdrelay R660 being restored at this time. Further it is noted that thehold relay R660 is of the slow-to-release type and restores shortlyafter the distributor 680 is released. Upon restoring, the hold relayR660 interrupts, at 'the contacts 662, the previously traced path forapplying ground potential to the controlconductor C610 of the trunk 615,ground potential being applied to the control conductor in` the localconnector switch 100 at this time. Further the hold relay R660interrupts, at the contacts 663, the previously mentioned multiplecircuits for energizing the lower windings of the switching relays R640and R650, the switching relay R640 being re' tained in its operatedposition at this. time due to the completed Aholding circuit forenergizing theintermediate winding thereof.

thereof in series with the upper winding of the transfer relay R130,this holding circuit extending from 'ground by way of the lower windingof R105, the contacts 106, 10| and 13|, and the upper` winding of R130to battery. Upon operating, the transfer relay R1|0 prepares, at the icontacts 1| I. a circuit traced hereinafter for energizing in multiplethe lower winding thereof and the rotary magnet M191 of the controlswitchv190; upon operatlng'the transfer relay R120 prepares, at thecontacts 125, a circuit Vtraced hereinafter for energizing in vmultiplethe lower winding thereof and the vertical magnet M111 of the mechanismy110; and upon operating, the transfer relay R130 prepares, at thecontacts 135, a circuit traced hereinafter'for energizing in multiplethe lower winding thereof and the rotary magnet M118 of the mechanism110. At this time the local connector switch 100 has been renderedresponsive to digits to be transmitted thereto from the telephonestation TI,

a loop circuit is completed for energizing in' .Y

series the upper and lower windings of the line relay R100 in the localconnector switch 100, this circuit extending from ground by way of thelower winding of R100, the line conductor C611 of thetrunk 615, thecontacts 654 and 643, C632 and the wiper 6I4 to the line conductor C601of the telephone line 605, and from battery by way of the upper windingof R100, the line conductor C616 of the trunk 615, the contacts 65| and64|, C63| and the wiper 6|3 to the line conductor C606 of the telephoneline 605, the line conductors C606 and C601 of the telephone line 605being connected together by way of the bridge path at the telephonestation TI. When the upper and lower windings of the line relay R100 arethus energized this relay operates to complete, at the contacts 102, acircuit for energizing the upper winding of the transfer relay R120,this circuit extending from ground by way of the contacts 102, thecontacts 104 of the set of switch springs S182 and the upper winding ofR120 to battery. When the upper winding of the transferrelay R120 isthus energized this relay operates to complete, at the contacts 124, anobvious multiple path for applying ground potential to the controlconductor C616 of the trunk 615, as previously noted. Also, uponoperating, the transfer relay R120 completes, at the contacts 123, acircuit for energizing in series the lower winding of the battery supplyrelay R105 and the upper winding -of the transfer relay R130,- thiscircuit extendingv from ground by way of the lower winding of R105, thecontacts 123 and the upper winding of R130 to battery. When the lowerwinding of the battery supplyv relay R105 and the `upper winding ferrelay R110, this circuit extending from ground by way of the set ofswitch springs S191, the

contacts 121 and the upper winding of R1|0 to battery. When the upperwinding of the transfer relay R1I0 is thus energized thisrelayopcrates'. Upon operating the battery supply relay R105 completes, atthe contacts 106, a holding circuit. for energizing the lower winding Inviewer the above description of the op! eration of the local finderswitch 600 under the control of the distributor 680 to find the callingtelephone line- 605 and the subsequent operation of the local connectorswitch incident to the seizure of the calling telephone line by thelocal iinder switch 600, it will be understood that these pieces ofapparatus `operate in substantially' the same manner regardless of theone hundred line group including the calling telephone line. In thepresent example the switching relay R640 in the local finder switch 600is operated due to the fact that the calling telephone line 605 isincluded in the first group of one hundred lines accessible to the localfinder switch 600. On the other hand, in the event the calling telephoneline 605 had been in the second group of one hundred lines the switchingrelay R650 would have been operated in a similar manner.

The subscriber at the telephone station TI then dials the first digit ofthe directory number of the called telephone station T2, thereby totransmit a first series of impulses by way of the subscriber loopcircuit to the line relay R100 in the local connector switch 100. It isnoted that the rst digit of the directory number of any telephonestation in the P. A. B. X, either 1 or 2, depending upon which onehundred line group includes the telephone line extending' to thetelephone station. In the present example the telephone line 150extending to the telephone station T2, is included in the-second groupof one hundred lines; accordingly, the rst digit dialed is the digit 2.The line relay R100 follows the dialed impulses in the usual manner,restoring each time the loop circuit is interrupted and operating eachtime the loop circuit is completed. Each time the line relay R100`restores it interrupts, at the contacts 102, the previously tracedcircuit for energizing the upper winding of the transfer relay R120 andcompletes, at the contacts 103, the previously mentioned circuit forenergizing in multiple the lower winding of the transfer relay R andtherotary magnet M191 of the control switch 190. The circuit for relayR100 operates it interrupts, at the ,contacts 103, the previouslytraced. circuit for energizing in multiple the lower winding of thetransfer relay R110 and the rotary magnet M191, and fcompletes, at thecontacts 102, the previously traced circuit for energizing the upperwindingA set of switch springs S191 is actuated into disengagement,thereby to interrupt the previously traced circuit for energizing theupper winding of the transfer relay R110; while the set of d switchsprings S108 is actuated into engagement, thereby to prepare a circuittraced hereinafter for energizing the release magnet M198. In thepresent instance the first.. digit comprises two impulses, thereby tocause the rotary magnet M191 to drive the wipers noted of the controlswitch 100 two steps in the counterclockwise direction.

At the conclusion of the rst digit the line relay R100 reoperates,thereby 'to cause' the transfer relay R110 to restore shortlythereafter. Upon restoring the` transfer relay R110 interrupts, at thecontacts 1 I 1, a further point in the previously traced circuit forenergizing in multiple the lower winding thereof and the rotary magnetM191, and prepares, at the contacts 112, the previously mentionedcircuit for energizing in multiple the lower winding of the transferrelay R120 and the verticaLmagnet M111.

The subscriber at the telephoneE station T1 then dials the second digitof the directory number of the called telephone station T2, thereby totransmit a second series of impulses by way of the subscriber loopcircuit to the line relay R100 in the local connector switch 100 in themanner previously explained.' As previously' noted the line relay R100follows the impulses. Each time the line relay R100 restores itcompletes, at the ontacts103, the previously menfer relay R120 and thevertical magnet M111 extends from ground by way-of the contacts 103, 112and 125 and the lower winding of R120 to battery, and from the contacts125 by way of the vertical magnet M111 to battery. On the other hand,each time the line relay R100 operates it interrupts, at thecontacts103, the previously traced circuit for energizing in multiple the lowerwinding of the transfer relay .R120 and the vertical. magnet M111. Thusthe transfer relay R120 remains operated during impulsing, this relaybeing of the slow-to-release type. Each time the vertical magnet M111 isenergized it operates to drive the first andsecond wiper sets of themechanism 110 one step in the vertical direction. When the rst andsecond wiper sets of the mechanism 110 are driven one step in thevertical direction away from their normal positions the sets of switchsprings S180, S182 and S185 are actuated. More particularly, the set ofswltchsprings S180 is-actuated into engagement, thereby to complete anobvious multiple path for applyingdg'round potential to the controlconductor C618 of the trunk 615;

vwhile the set of switch springsS185 is actuated into engagement,thereby to prepare a circuitY traced hereinafter for energizing therelease magnet M119. The contacts 184 of the set of switchv springs S182are actuated into disengagement, thereby to interrupt the previouslyltraced circuit for energizing the upper winding of the transfer relayR120; while the contacts 183 of the set of switch springs S182 areactuated into engagement, thereby to prepare a circuit tracedhereinafter for energizing the winding of the switching relay R160.

At the conclusion of the second digit the line relay R reoperates,thereby to cause the transfer relay R to restore shortly thereafter.Upon restoring the transfer relay R120 interrupts, at the contacts 125,a further point in the previously traced circuit for energizing inmultiple the lower winding thereof and the vertical magnet M111, andprepares, at the'contacts 128, a point in the previously mentionedcircuit for energizingin multiple the lower winding ofthe transfer relayR and the rotary magnet M110.

rEhe subscriber at the telephone station TI then dials the third digitof the directory number of the called telephone station T2, thereby totransmit a third series of impulses by way of the subscriber loopcircuit tofthe line relay R100 in the local connector switch 100 in themanner previcusly explained. As previously noted the line relay R100follows the impulses. Each time the line relay R100 restores itcompletes, at the contacts 103, the previously mentioned circuit forenergizing in multiple the lower winding of the transfer relay R130 andthe rotary magnet M110. The circuit for energizing in multiple the lowerwinding of the transfer. relay R130 and the rotary magnet M118 extendsfrom ground by way of the contacts 103, 112, 126 and 135 and the lowerwinding of R130 to battery, and from the contacts by way of the rotarymagnet M118 to battery; On the other hand, each time the line relay R100operates it interrupts, at the contacts 103, the previously tracedcircuit for energizing in multiple the lower winding of the transferrelay R130 and the rotary magnet M118. Thus the transfer relay R130remains operated dur.'

ing irnpulsing, this relay being of the slow-torelease type. Further itis noted that when the line relay R100 restores upon the first impulseof the third digit it interrupts, at the contacts 101, the previouslytraced holding circuit for energizing in series the lower winding of thebattery supply relay R105 and the upper winding ofthe transfer relayR130, the original circuit for energizing in series the lower winding ofthe battery supply relay R105 and the upper winding of the transferrelay R130 being interrupted at the contacts 123 due to the restoredcondition of the transfer relay R120 at this time. Also upon restoring,the transfer relay R120 interrupts, at the contacts 124, the previouslymentioned path for applying ground potential to the controlconductorC618 of the trunk 615, ground potential being applied to thecontrol conductor C618 of the trunk 615 due to the operated condition ofthe set ofswitch springs S at this time.

Each time the rotary magnet M118 is energized it operates to drive therst and second wiper sets of the mechanism 110 one step in the rotarydirection.

4At the conclusion of the third digit the line circuiting the winding ofthe busy relay R140.v

relay R100 reoperates, thereby to cause the transfer relay R130 torestore shortly thereafter. Prior to the restoration of the transferrelay R130 and at the conclusion of the third digit the first and secondwiper sets of the mechanism 110 engage corresponding lines in the rstand second sections of the main contact bank, Y,whereupon a test circuitfor the busy relay R140 is completed. This test circuit extends frombattery by way of the winding of R140, the contacts 133, C1|5, the wiper193 and engaged second contact in the associated contact bank 194 of'the control switch 190, C149 and the control wiper 116 of the secondWiper set to the control conductor C153 of the telephone line 150extending to the telephone station T2. In the event the telephonestation T2 is busy at this time, ground potential appears upon thecontrol conductor C153 of the telephone line 150, thereby to complete acircuit identical to the test circuit previously traced for energizingthe Winding of the busy relay R140, thereby to cause the latter relay tooperate. Upon'operating, the busy relay R140 prepares, at the contacts144, a holding circuit traced hereinafter for `energizing the windingthereof. Upon restoring the transfer relay R130 interrupts, at thecontacts'133, the previously traced operating circuit for energizing thewinding of the busy relay R140 and completes, at the.

contacts 134, the previously mentioned holding circuit for energizingthewinding of the busy relay R140. The holding circuit for `energizingthe winding of the busy relay R140 extends from the grounded controlconductor C618 of the trunk 615 by way of the contacts 144 and 134 andthe winding of R140 to battery. V'

Also upon operating, the busy relay R140 interrupts, at the contacts 14|and 143, points in a circuit tracedhereinafter for projecting ringingcurrent over the telephone line 150 extending to the calledtelephonestation T2. Finally upon operating, the busy relay R140 completes, atvthe contacts 142,/a circuit for returning busy tone current over theloop circuit to the calling telephone station TI, this circuit extendingfrom the ungrounded terminal of a grounded source of busy current by Wayof the conductor C104, the

l contacts 12|,142 and 153 and the condenser 108 vbusy tone at thistime, thereby to indicate to the subscriber thereat that the connectioncannot immediately be had due to the busy condition of the calledtelephone station T2. f

The subscriber at the calling telephone station T| then releases Atheline circuit 690, the local finder switch 600 and the local connectorswitch 100 by replacing the receiver ofthe telephone instrument thereatupon its switchhook in a manner more fully described hereinafter.

Accordingly. the busy relay R140 `does not operate at this time. Hence,when the transfer relay R130 restores it interrupts, at the contacts133,

j the contacts l132, C1|5, vthe `rwiper 193 and enthe previously tracedtest circuit for the busy relay R140 and completes, at the contacts 132,a path for applying ground potential to the control conductor C153 ofthe telephone line 1.50 extending to the called telephone station T2,this path extending from ground by way of the wiper 19| and engagedsecond contact in the associated contact bank 192 of the control switch190, C1|6,

gaged second contact in the associated contact bank 194 of the controlswitch 190, C149 and the of the telephone line 150 causes the linecircuit individually associated therewith to operate, thereby to markthe telephone line 1.50 extendingto the called telephone station T2 asbusy.

Also upon restoring, the transfer relay R130com- 'pletes, at thecontacts 131, a circuit for energizing the winding of the switchingrelay R160, this circuit extending from ground by way. of the contacts102, the contacts 183 of theset of switch springs S182, C1I3, thecontacts` 131, the wiper 195 and engaged second contact in theassociated contact bank/196 of the control switch 190 and the winding ofR160 to battery. gized over the above-traced circuit the switching relayR160 operates to complete, at the contacts 163,'an obvious alternativepath for applying ground potential to the control conductor C153 of thetelephone line 1.50 and to interrupt, at the contacts 164, a point inthe previously v mentioned circuit for energizing in multiple the theungrounded terminal of a grounded sourceof ringing current by way of theconductor C101, the contacts 143 and 154, C141, the contacts 162 and thewiper 11.5' to the line conductor C152 of lthe telephone line 150, andfrom battery by way of the lower winding of the cutoiI relay R150, thecontacts 14| and v15|,'C146, the contacts16| and the wiper 114 to theline conductor C15| of the telephone line 150, the ringer at the calledtelephone station T2 being connected across the line conductors C15| andC152 ofthe telephone line 150. Accordingly, the ringer at the calledtelephone station T2 is operated at this time,

When the subscriber at the called telephone station` T2 answers the callby removing the receiver of the telephone instrument thereat fromitsswitchhook av circuit substantially identical to that previously tracedlfor projecting ringing current over the telephone line is completedforenergizing the lower lwinding of the cutoif relay R150. When thelower winding of the cutoff relay R150 is thus energized thisrelay'operates shortly thereafter, this relay be- On the other hand,inthe event the called telephoneJ station T2 'is idle when the localconnector switch 106 operates to seize the telephone line 150 extendingthereto in the' manner previously explained, battery potential appearsupon the control conductor C153 of the telephone line 150, thereby tocomplete a circuit identical to thetest circuit previously traced forshort- 154, the previously traced circuit for projecting Whenenerringing current over the telephone line 150 ex'- v andl the calledtelephone station T2. This loop` circuit extends from ground by way ofthe lower winding of R105, the contacts 122 and 155, C101, l thecontacts 162 and the wiper 115,.,to the line conductor` C152 of thetelephone line 150 and from battery by way of thel upper winding ofR105. the contacts 152, C146, the contacts 16| and the wiper 110 to thelline conductor C15! of the telephone line 150the telephone instrument atthe called telephone lstation T2 being connected across the lineconductors 015| and C152 of the telephone line 150 at this time.Accordingly, talking battery is supplied to the telephone instrument atthe calling telephone station Tl from the line relay R100, while talkingbattery is supplied to the telephone instrument at the called telephonestation T2 from the battery supply relay R105. Finally, it is noted thatthe loop circuit extending -to the calling telephone station T| isinterconnected with a. loop circuit extending to the called telephonestation T2 by the condensers 106 and 109, thereby to complete a two-waycommunication connection between the calling telephone station Tlv andthecalled telephone station T2.

'I'he release of the established connection between the callingtelephone station Tl and the called telephone station T2 is primarilyunder the control of the subscriber at the calling telephone station Tiand when the receiver of the telephone instrument at the callingtelephone l station TI is replaced uponVl its switchhook the .previouslytraced loop circuit for energizing the windings of the line relay R100is interrupted, thereby'to cause the ,latter relay to restore. Also,when the receiver of the telephone instrument at the called telephonestation T2 is replaced upon its switchhook the previously traced loopcircuit for energizing the windings of the battery supply relay R105 isinterrupted, thereby to cause the latter relay to restore. Uponrestoring, the line relay R100 interrupts, at the. contacts 102, thepreviously traced circuit for energizing the Winding of the switchingrelay R160, thereby to cause the latter relay to restore shortlythereafter, the latter relay being of the slow-to-release type. Uponrestoring, the switching relay R160 completes, at the contacts 169, thepreviously mentioned circuit for energizing in multiple the releasemagnet-M119 and the release magnet M198, this circuit extending fromground by way of the contacts 103, 1|2, 126,-136, 169 and 169, the setof switch springsoS185 and the release magnet M119 to battery, and fromthe contacts 166-by way of the set of switch springs S198 and therelease magnet M198 to battery. When thus energized the reiease magnetsM119 and yM198 operate.

Upon operating the release `magnet M198 releases the wipers` noted ofthecontrol switch 190 and causes these" wipers to be returned to theirnormal positions. When the wipers noted of the control switch 190 arereturned to their normal positions the sets of switch springs S191 andS198 are actuated. More particularly, the set of 4 switch springs S191is actuated into engagement,

thereby to prepare the previously traced circuit for energizing theupper winding of the transfer relay R1I0; while the set of switchsprings S198 is actuated into disengagement, thereby to inter rupt thepreviously traced circuit for energizing the release magnet M198. u

Upon operating, the release magnet M119 releases the rst and secondwiper sets of the mechanism 110, thereby to cause these wiper sets to bereturned to their normal ,positions When the wiper sets of the mechanismare returned to their normal positions the sets of switch springs S160,S182 and S185 are actuated. More particularly, the set of switch springsS is actuated ito disengagement, thereby to interrupt the previouslymentioned path for applying ground potential to the control conductorC618 of the trunk 615; while the set of switch springs S is actuated-into disengagement, thereby to interrupt the previously traced circuitfor energizing the release magnet M119. Finally the contacts 163 and 186of the set o f switch springsy S182 are respectively actuatedintodisengagement and into' engagement, thereby respectivelyV to interrupt afurther point in the previously' traced circuit for energizing `thewinding of the switching relay R160 andl to prepare a point in thepreviously traced circuit for energizing the Y upper winding of thetransfer relay R120. When the switching relay' R160 restores thepreviously traced paths for applying ground' potential to the controlconductor C159 of the telephone line 150 are interrupted, vthereby tocause the line circuit individually associated with the telephone line150 to operate in order to mark the telephone line 150 as idle. Alsowhen ground potential is removed from the controlcpnductor C618 of thetrunk 615 the previously; traced holding circuit for energizing theintermediate winding o'f the line and cutoff relay R690 is interrupted,thereby to cause the latter relay to restore. Upon restoring, the lineand cutoi relay R690 interrupts, at the contacts 693, a further point inthe previously traced path for applying ground potential to the controlconductor C609 of the telephone line 605 extending to the telephonestation TLthereby to mark the telephone line 605 as'idle.

Finally, when ground potential is removed from the control conductorC618 of the trunk A 615 the previously traced holding circuit forenergizing the intermediate winding of the switching relay R660 isinterrupted, thereby to cause the latter relay to restore, and complete,at the contacts 698, the previously mentioned circuit for energizing therelease magnet M625, this circuit extending from ground by way of thevcontacts 66|, the contacts. 621 of the set of switch springs S625, thecontacts 65| and 648 and the release magnet M625 to battery. When thusenergized the release magnet M625 operates to release the rst and secondwiper sets A626 of the set of switch springs S625 are actuated. intoengagementl therebyto complete the previously traced path ior applyingground potential to the all-link-busy conductor C681 extending to thedistributor 600. Thisapplication of ground potential to theall-lin'k-busy con` ductor C68I- extending to the distributor 680renders the .distributor 680 operative to preselect for use an idle oneof the local links. Also contacts 629 of the set of switch springs S621.

are actuated into engagement, .thereby to connect the control conductorlC618 of the trunk 615 to the guard conductor C683 extending to thedistributor 680.

At this time the 1oa1 ander switch son and' the local connector switch100 of the local link illustrated are completely released, thereby torender this local link available for further use.

vthe contacts 628 of the vset of switch springs lS621 are actuated intodisengagement, thereby to Also the line circuit 690 individuallyassociated Y with the telephone line 605 is restored, thereby to-markthe telephone line 605 extending to the telephonestatin Ti as idle.Similarly, the line.

ycircuit individually associated with the telephone line 150 isrestored, thereby to mark the telephone line 150 extending to thetelephone station T2 as idle. A

Information call from a 4'station to the operator position inthe P. A.B. X

An information call which is to be extended from one of the stations tothe operator position in the P. A. B. X is initiated at the-callingstation by removing the receiver of the telephone vinstrument thereatfrom its switchhook'. For

example, in extending an infomation call from the telephone station TIto the operatorposition 800 the call is first initiated at the station-Tl by removing the receiver of the telephone instrument thereat fromits switchhook, thereby to cause the line circuit 690 individuallyassociated with the telephone line 605 extending to,the callingtelephone station TI to operate as previously explained. Upon operating,the line circuit 690 initiates operation of the distributor 680,whereupon the vdistributor 680 assigns the previously selected locallink, such, for example, as the local link illustrated, to the use ofthe calling telephone station TI and causes the local finder switch 600of the local link illustrated to seize the telephone line 605 extendingto the calling telephone station TI in the previously described manner.After the local finder switch` 600 of the local link illustrated seizesthe telephone line 605 extending to the calling telephone station Tl,the distributor 680 operates to preselect anotherone ofthe idle locallinks to the use of acalling telephone station as. previously explained.Also, when the local nder switch 600 seizesy the telephone line 605,extending to the calling telephone station TI, a loop circuit iscompleted between the line relay R in the local connector switchpreviously explained, whereupon the local connector switch 100 isrendered responsive to digits transmitted from "the calling telephonesta-'v 100 and the calling telephone station Tl as in the line circuit690 occupies-its operated position; while the switching relay R640 inthe local iinder switch 600 occupies its operated position. Also, in thelocal connector switch 100 theline relayjR100, the transfer relays R1I0,R120 and yR and the battery'supply relay R105 occupy contacts 102, thelpreviously traced circuit for energizing the'upper winding of thetransfer relay R120 and completes, at the contacts 103,l l thepreviously traced multiple. circuit for energizing the lower winding ofth transfer relay R110 and the rotary magnet M191 of'thefcontrol switch190. On the `other hand, each time the line relay R100 operates, itinterrupts, at the contacts 103, the previously traced .circuit forenergizing in multiple the lower, winding or the transfer relay and-therotary magnet M191 and completes, at the contacts 102, the lpreviouslyItraced circuit for energizing the upper winding of the transfer relayR120.' Thus, during impulsing, the transfer vrelays R1I0 and R120 remainoperated.

' fer relay R110 torestore shortly thereafter.

Accordingly, at this time, the rotary magnet M191 is successivelyenergized three times. thereby to cause the wipers noted of the controlswitch v to be driven in the counterclockwise/direction into engagementwith the third contacts in the associated contact banks. Also, when thewipers noted of the control switch 190 are driveri one step in thecounterclockwise direction away from their normal positions, the'sets ofswitch springs S191 and S198 are actuated.I More particularly, the setof switch springs S191 is actuated into f disengagement, thereby tointerrupt the previously traced circuit for energizing the upper windingof the transfer relay R110; while the set of switch A springs S198 isactuated into engagement, Ythereby to prepare the previously tracedcircuit for energizing the release magnet, M198 of the control switch190.

At the lconclusion of the single digit, the line relay R100 reoperates,thereby to .cause the trans- At this time no further digit-s are dialedat the calling telephone station TI and the operation of the controlswitch 190 is effective to complete a circuit for energizing the windingof the pilot relay R980 and a path fory applying battery potential tothe marking conductor C921 included in a group of conductors extendingbetween the local link illustrated and the operator nder switch 900. Thecircuit for energizing the winding of the pilot relay R980 extends fromground by way of the wiper 19| and engaged third contactin theassociated contact bank 192 of the control switch. 190, C1I0l and thewinding of R980l to battery; andthe path for applying battery potentialto the marking conductor C921 extends from battery by way of the winding'of the busy relay R140, the contacts 133, C1I5 and the wiper 193 andengaged third contact in the associatedcontact b ank '|94 of the controlswitch 190 to the marking conductor C9121. The application of batterypotential to the marking conductor C921

